1. Field of the Invention
This invention relates to rubber compositions suitable for use particularly in the tread portion of a tire. More particularly, the invention is directed to the provision of such a composition comprised of a selected rubber combined with a selected type of carbon black of specified particle characteristics.
2. Description of Prior Art
Tires for sophisticated sports cars are required to meet high mechanical strength and driving stability. To attain improved stability, an approach has been proposed to cope with this trend with the use of a tread rubber of high tan .delta. at 0.degree. C. and 60.degree. C. This quality is closely associated with the gripping force of the tire on the road surface.
To increase tan .delta. at 0.degree. C. and 60.degree. C., polymeric rubbers of high glass transition temperatures (Tg) have been used which are selected for instance from styrene-butadiene copolymer rubbers abundant in styrene content or 1,2-vinyl content. Alternatively, large amounts of carbon black have been incorporated with a selected starting rubber.
High Tg rubbers, however, are not wholly satisfactory as they are rather dependent on temperature conditions, insufficiantly hard and rigid at elevated temperature and inadequate in road gripping and are reduced in mechanical strength.
Too much carbon black fails to become homogeneously dispersible, rendering the finished rubber composition mechanically weak.